Genetic defects cause 20-40 percent of all epilepsies. Several types of inherited epilepsy appear to be linked to nicotinic receptors. However, autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is the only one that has been linked to specific nicotinic mutations -alpha4(S248F), alpha4(777ins3), and alpha4(S252L). These mutations produce brief, repetitive seizures that occur primarily during phase 2 sleep. The mechanism of seizure generation has not been established. We hypothesize that a reduction in Ca2+-induced potentiation of the acetylcholine (ACH) response causes ADNFLE seizures. Our preliminary data show that all three presently identified ADNFLE mutations reduce Ca2+ potentiation of the ACH response. However, previous studies show that the alpha4(S248F) mutation also reduces the Ca2+ permeability of the receptor relative to Na+ (Pca/PNa) and, that the alpha4(S248F) and alpha4(777ins3) mutations enhance ACh-induced receptor desensitization. Aim 1 is to determine whether reduced Ca2+ potentiation is the only common functional effect of the ADNFLE mutations. We will express rat versions (S252F, +L264, S256L) of the human ADNFLE mutations with wild-type (WT) rat beta2 subunits in Xenopus oocytes and examine their effects on desensitization, surface expression, receptor turnover, and choline potentiation of the ACH response. Aim 2 is to determine whether all three ADNFLE mutations reduce the Pca/PNa and Ca2+ influx through the receptors. Aim 3 is to demonstrate that the ADNFLE mutations reduce Ca2+ potentiation by enhancing Ca2+ block of the receptor rather than by reducing Ca2+ potentiation per se. Aim 4 is to characterize the mechanism of mutant-induced reductions in Ca2+ potentiation at the single-channel level. Our results should elucidate the connection between central nicotinic receptors and epileptic seizures.